Wireless communication systems, interrogators and methods of communicating within a wireless communication system

ABSTRACT

The present invention relates to wireless communication systems, interrogators and methods of communicating within a wireless communication system. One aspect of the present invention provides a wireless communication system including at least one remote communication device configured to communicate a return link wireless signal; an interrogator including: a communication station configured to receive the return link wireless signal and to generate a return link communication signal corresponding to the return link wireless signal; communication circuitry coupled with the communication station and configured to communicate the return link communication signal; and a housing remotely located with respect to the communication station and including circuitry configured to receive the return link communication signal from the communication circuitry and to process the return link communication signal.

TECHNICAL FIELD

The present invention relates to wireless communication systems,interrogators and methods of communicating within a wirelesscommunication system.

BACKGROUND OF THE INVENTION

Electronic identification systems typically comprise two devices whichare configured to communicate with one another. Preferred configurationsof the electronic identification systems are operable to provide suchcommunications via a wireless medium.

One such configuration is described in U.S. patent application Ser. No.08/705,043, filed Aug. 29, 1996, assigned to the assignee of the presentapplication, and incorporated herein by reference. This applicationdiscloses the use of a radio frequency (RF) communication systemincluding communication devices. The disclosed communication devicesinclude an interrogator and a remote transponder, such as a tag or card.Another example of a wireless communication system including abackscatter system is described in U.S. Pat. No. 5,649,296 to MacLellanet al. which is also incorporated herein by reference.

Such communication systems can be used in various applications such asidentification applications. The interrogator is configured to output apolling or interrogation signal which may comprise a radio frequencysignal including a predefined interrogation code using which theinterrogator may address remote transponders. The remote transponders ofsuch a communication system are operable to transmit an identificationsignal responsive to receiving an appropriate polling or interrogationsignal.

More specifically, the appropriate transponders are configured torecognize the predefined code. The transponders receiving the code cansubsequently output a particular identification signal which isassociated with the transmitting transponder. Following transmission ofthe polling signal, the interrogator is configured to receive theidentification signals enabling detection of the presence ofcorresponding transponders.

Such communication systems are useable in identification applicationssuch as inventory or other object monitoring. For example, a remoteidentification device can be attached to an object of interest.Responsive to receiving the appropriate polling signal, theidentification device is equipped to output an identification signal.Generating the identification signal identifies the presence or locationof the identification device and the article or object attached thereto.

It may be desired to communicate with remote communication deviceslocated at greater distances in particular applications. Such areas mayexceed the range of the communication system. Typical conventionalarrangements require the utilization of numerous interrogators forcommunication with the remote communication devices in such spacedareas. Alternatively, the movement of a single interrogator from onearea to another is required.

SUMMARY OF THE INVENTION

The present invention provides wireless communication systems,interrogators and methods of communicating within a wirelesscommunication system.

According to one aspect of the present invention, a wirelesscommunication system comprises at least one remote communication deviceconfigured to communicate a return link wireless signal. The return linkwireless signal comprises a radio frequency signal in certain aspects ofthe invention.

The wireless communication system in some embodiments includes aninterrogator having a communication station, communication circuitry anda housing. The communication station is configured to receive the returnlink wireless signal and to generate a return link communication signalcorresponding to the return link wireless signal. The communicationcircuitry is provided to couple with the communication station and tocommunicate the return link communication signal. The housing isremotely located with respect to the communication station and includescircuitry configured to receive the return link communication signalfrom the communication circuitry and to process the return linkcommunication signal.

In one configuration, the housing includes automatic gain controlcircuitry configured to adjust the power level of the return linkcommunication signals. Amplifiers can be provided within one or both ofthe interrogator housing and the communication station to increase thepower level of the return link communication signals. Pluralcommunication stations and plural communication circuits are coupledwith a single interrogator housing in some embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a block diagram of an exemplary communication system accordingto one embodiment of the present invention.

FIG. 2 is a front view of a wireless remote communication deviceaccording to one embodiment of the invention.

FIG. 3 is a front view of an employee badge according to anotherembodiment of the invention.

FIG. 4 is a functional block diagram of a transponder included in theremote communication device of FIG. 2.

FIG. 5 is a functional block diagram of one embodiment of a portion ofan interrogator of the invention.

FIG. 6 is a functional block diagram of one embodiment of an RF sectionof the interrogator of FIG. 5.

FIG. 7 is a functional block diagram of exemplary communicationcircuitry shown in FIG. 1.

FIG. 8 is a functional block diagram of exemplary transmit circuitry ofa communication station shown in FIG. 1.

FIG. 9 is a functional block diagram of exemplary receive circuitry ofthe communication station shown in FIG. 1.

FIG. 10 is a functional block diagram of exemplary adjustment circuitrywithin a housing of the interrogator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

FIG. 1 illustrates a communication system 10 embodying the invention.Communication system 10 comprises an electronic identification system inthe embodiment described herein. Communication system 10 may beconfigured for backscatter communications as described in detail below.Other communication protocols are utilized in other embodiments.

The depicted communication system 10 includes a plurality of remotecommunication devices 12 and an interrogator 26. Wireless (e.g., radiofrequency) communications can occur intermediate remote communicationdevices 12 and interrogator 26 for use in identification systems andproduct monitoring systems as exemplary applications.

Remote communication devices 12 can include radio frequencyidentification devices (RFID) or remote intelligent communication (RIC)devices in the embodiments described herein. Exemplary remotecommunication devices 12 are disclosed in U.S. patent application Ser.No. 081705,043. Plural remote communication devices 12 typicallycommunicate with interrogator 26.

In one embodiment, remote communication devices 12 individually comprisea wireless identification device such as the MicroStamp (™) integratedcircuit available from Micron Communications, Inc., 3176 S. Denver Way,Boise, Id. 83705. Such a remote communication device 12 can be referredto as a tag or card as illustrated and described below.

Remote communication devices 12 are configured to interface withinterrogator 26 using a wireless medium in one embodiment. Morespecifically, communications intermediate remote communication devices12 and interrogator 26 occur via an electromagnetic link, such as aradio frequency link in the described embodiment. Exemplarycommunications occur at microwave frequencies. Other configurations forcommunication are possible.

As described in detail below, interrogator 26 is configured to outputforward link communications. Further, interrogator 26 is operable toreceive reply or return link communications from remote communicationdevices 12 responsive to the outputting of forward link communications.In accordance with the above, forward link communications and returnlink communications comprise wireless signals, such as radio frequencysignals, in the described embodiment. Other forms of electromagneticcommunication, such as infrared, acoustic, etc., are possible.

The depicted configuration of communication system 10 illustratesinterrogator 26 communicating with a plurality of remote communicationdevices 12 located in a plurality of corresponding communication ranges15, also referred to as read zones. The depicted interrogator 26includes a housing 14 coupled with a plurality of communication paths 17individually positioned and configured to communicate with remotecommunication devices 12 located within corresponding communicationranges 15. Communication paths 17 individually include communicationcircuitry 106 and a corresponding communication station 120 in thedescribed embodiment.

As described in detail below, housing 14 of interrogator 26 includescircuitry (not shown in FIG. 1) configured to generate a plurality offorward link communication signals. Such forward link communicationsignals are communicated within communication circuitry 106 of selectedcommunication paths 17 to respective communication stations 120 havingantennas X1, X2 . . . XN. Such communication stations 120 are configuredto emit forward link wireless signals 27 which correspond to the forwardlink communication signals. In addition, communication stations 120 canindividually emit a continuous wave signal during backscatter mode ofoperations of communication system 10. Further transmit operations ofinterrogator 26 are described in a copending U.S. patent applicationfiled the same day as the present application, having the title“Wireless Communication Systems, Interrogators and Methods ofCommunicating Within a Wireless Communication System”, assigned toassignee hereof, having attorney docket number MI40-179, naming DavidOvard and Roy Greeff as inventors, and incorporated herein by reference.

As illustrated, communication stations 120 are preferably configured toradiate the forward link wireless signals 27 to associated remotecommunication devices 12 within respective communication ranges 15.Responsive to the reception of forward link wireless signals 27,individual remote communication devices 12 are operable to reply withreturn link wireless signals 29.

Communication stations 120 also include plural receive antennas R1, R2 .. . RN which are configured to receive return link wireless signals 29from remote communication devices 12. Communication stations 120 ofinterrogator 26 preferably individually include receive circuitryconfigured to receive the return link wireless signals 29 and applyreturn link communication signals to interrogator housing 14 forprocessing as described in detail below. In particular, communicationstations 120 generate return link communication signals corresponding tothe received return link wireless signals. Communication circuits 106communicate the return link communication signals to interrogatorhousing 14.

FIG. 1 is an illustrative representation of wireless communicationsystem 10. More specifically, communication ranges 15 may be spread outover a relatively large geographic range. The wireless communicationsystem 10 of the present invention provides the advantages of utilizinga single interrogator housing 14 and associated communication circuitrytherein to communicate with remote communication devices 12 located inplural communication ranges 15.

Further, wireless communication system 10 of the present inventionpermits a single interrogator housing 14 and associated circuitry toservice multiple communication ranges 15 which may be located severalhundred feet apart or further, or in harsh environments. For example,one interrogator housing 14 can be utilized to service read zones orcommunication ranges 15 within spaced warehouses. Individualcommunication ranges 15 may be spaced from one another at distanceswhich exceed the communication range of the devices. Additionally,adjacent communication ranges 15 may overlap in some applications.

As previously mentioned, individual communication paths 17 includecommunication circuits 106 and associated communication stations 120.Communication stations 120 are preferably positioned to communicate withrespective communication ranges 15. Communication circuits 106 areconfigured in the depicted arrangement to communicate forward linkcommunication signals from interrogator housing 14 to correspondingcommunication stations 120. Communication circuits 106 are alsoconfigured to communicate return link communication signals receivedwithin corresponding communication stations 120 to interrogator housing14.

In the described embodiment, communication circuits 106 are locatedoutside of interrogator housing 14. In addition, communication stations120 are remotely located with respect to interrogator housing 14.Communication stations 120 are individually configured to receiveforward link communication signals from interrogator housing 14 viacommunication circuitry 106 and radiate forward link wireless signals 27corresponding to the forward link communications signals usingassociated antennas X1, X2 . . . XN.

Further, communication stations 120 are individually configured toreceive return link wireless signals 29 from remote communicationdevices 12 using associated antennas designated R1, R2 . . . RN.Communication stations 120 output return link communication signalscorresponding to the return link wireless signals 29 to interrogatorhousing 14 using respective communication circuits 106.

Individual ones of communication stations 120 may be located at varyingdistances from interrogator housing 14 depending upon a particularapplication. Interrogator housing 14, communication circuits 106 andcommunication stations 120 are configured to communicate the forwardlink communication signals and return link communication signalsintermediate interrogator housing 14 and respective communicationstations 120 regardless of the varying distances.

Remote communication devices 12 are individually configured for wirelesscommunications in one embodiment as described in detail below. Suchremote communication devices 12 receive the forward link wirelesssignals 27 and respond with the return link wireless signals 29 whichare received within communication stations 120.

In one embodiment, return link wireless signals 29 are encoded withinformation that uniquely identifies or labels the particular device 12that is transmitting so as to identify any object, animal or person withwhich communication device 12 is associated. More specifically, remotedevices 12 are configured to output an identification signal withinreturn link wireless signals 29 responsive to receiving forward linkwireless signals 27. Interrogator 26 is configured to receive andrecognize the identification signal within the return or return linkcommunications 29. The identification signal can be utilized to identifythe particular transmitting remote communication device 12.

Referring to FIG. 2, one embodiment of a remote communication device 12is illustrated. The depicted communication device 12 includes atransponder 16 having a receiver and a transmitter as described below.Communication device 12 further includes a power source 18 connected totransponder 16 to supply operational power to transponder 16. In theillustrated embodiment, transponder 16 is in the form of an integratedcircuit 19. However, in alternative embodiments, all of the circuitry oftransponder 16 is not necessarily included in integrated circuit 19.

Power source 18 is a thin film battery in the illustrated embodiment,however, in alternative embodiments, other forms of power sources can beemployed. If the power source 18 is a battery, the battery can take anysuitable form. Preferably, the battery type will be selected dependingon weight, size and life requirements for a particular application. Inone embodiment, battery 18 is a thin profile button-type cell forming asmall, thin energy cell more commonly utilized in watches and smallelectronic devices requiring a thin profile. A conventional button-typecell has a pair of electrodes, an anode formed by one face and a cathodeformed by an opposite face. In an alternative embodiment, the batterycomprises a series connected pair of button type cells.

Communication device 12 further includes at least one antenna connectedto transponder 16 for wireless transmission and reception. In theillustrated embodiment, communication device 12 includes at least onereceive antenna 44 connected to transponder 16 for radio frequencyreception by transponder 16, and at least one transmit antenna 46connected to transponder 16 for radio frequency transmission bytransponder 16. The described receive antenna 44 comprises a loopantenna and the transmit antenna 46 comprises a dipole antenna.

Remote communication device 12 can be included in any appropriatehousing or packaging. FIG. 2 shows but one example of a housing in theform of a miniature housing 11 encasing device 12 to define a tag whichcan be supported by an object (e.g., hung from an object, affixed to anobject, etc.).

Referring to FIG. 3, an alternative housing is illustrated. FIG. 3 showsa housing in the form of a card 13. Card 13 preferably comprises plasticor other suitable material. Plastic card 13 houses communication device12 to define an employee identification badge including thecommunication device 12. In one embodiment, the front face of card 13has visual identification features such as an employee photograph or afingerprint in addition to identifying text.

Although two particular types of housings have been disclosed, thecommunication device 12 can be included in any appropriate housing.Communication device 12 is preferably of a small size that lends itselfto applications employing small housings, such as cards, miniature tags,etc. Larger housings can also be employed. The communication device 12,provided in any appropriate housing, can be supported from or attachedto an object in any desired manner.

FIG. 4 is a high level circuit schematic of an embodiment of transponder16 utilized in remote communication devices 12. In the embodiment shownin FIG. 4, transponder 16 is implemented within a monolithic integratedcircuit 19. In the illustrated embodiment, integrated circuit 19comprises a single die, having a size of 209×116 mils², including areceiver 30, a transmitter 32, a microcontroller or microprocessor 34, awake up timer and logic circuit 36, a clock recovery and data recoverycircuit 38, and a bias voltage and current generator 42. Integratedcircuit 19 preferably comprises a small outline integrated circuit(SOIC) package. Receiver 30 and transmitter 32 comprise wirelesscommunication circuitry configured to communicate wireless signals.

In one embodiment, communication devices 12 switch between a “sleep”mode of operation, and higher power modes to conserve energy and extendbattery life during periods of time where no interrogation signal 27 isreceived by devices 12, using the wake up timer and logic circuitry 36.

In one embodiment, a spread spectrum processing circuit 40 is includedin transponder 16. In this embodiment, signals transmitted and receivedby interrogator 26 and signals transmitted and received by communicationdevice 12 are modulated spread spectrum signals. Many modulationtechniques minimize required transmission bandwidth. However, the spreadspectrum modulation techniques employed in the illustrated embodimentrequire a transmission bandwidth that is up to several orders ofmagnitude greater than the minimum required signal bandwidth. Althoughspread spectrum modulation techniques are bandwidth inefficient insingle user applications, they are advantageous where there are multipleusers, as is the case with the preferred radio frequency identificationcommunication system 10 of the present invention.

The spread spectrum modulation technique of the illustrated embodimentis advantageous because the interrogator signal can be distinguishedfrom other signals (e.g., radar, microwave ovens, etc.) operating at thesame frequency. The spread spectrum signals transmitted by communicationdevice 12 and interrogator 26 are pseudo random and have noise-likeproperties when compared with the digital command or reply. Theillustrated embodiment employs direct sequence spread spectrum (DSSS)modulation.

In operation, interrogator 26 sends out a command that is spread arounda certain center frequency (e.g, 2.44 GHz). After the interrogatortransmits the command, and is expecting a response, the interrogatorswitches to a continuous wave (CW) mode for backscatter communications.In the continuous wave mode, interrogator 26 does not transmit anyinformation. Instead, the interrogator just transmits a radio frequencycontinuous wave signal. In the described embodiment, the continuous wavesignal comprises a radio frequency 2.44 GHz carrier signal. In otherwords, the continuous wave signal transmitted by interrogator 26 is notmodulated. After communication device 12 receives the forward linkcommunication from interrogator 26, communication device 12 processesthe command.

If communication device 12 is operating in a backscatter mode, device 12modulates the continuous wave signal providing a modulated continuouswave signal to communicate return link communication 29 responsive toreception of forward communication signal 27. Communication device 12may modulate the continuous wave signal according to a subcarrier ormodulation signal. Modulation by device 12 comprises selectivereflection of the continuous wave signal. In particular, device 12alternately reflects or does not reflect the continuous wave signal fromthe interrogator to send its reply. For example, in the illustratedembodiment, two halves of a dipole antenna are either shorted togetheror isolated from each other to send a reply. Alternatively,communication device 12 can communicate in an active mode.

The modulated continuous wave signal communicated from device 12comprises a carrier component and plural side band components about thecarrier component resulting from the modulation. More specifically, themodulated continuous wave signal output from device 12 includes a radiofrequency continuous wave signal having a first frequency (2.44 GHz),also referred to as a carrier component, and a subcarrier modulationsignal having a different frequency (e.g., 600 kHz) which provides theside band components. In particular, the side band components are at+/−600 kHz of the carrier component.

In one embodiment, the clock for transponder 16 is extracted from theincoming message itself by clock recovery and data recovery circuitry38. This clock is recovered from the incoming message and used fortiming for microcontroller 34 and all the other clock circuitry on thechip and also for deriving the transmitter carrier or the subcarrier,depending on whether the transmitter is operating in active mode orbackscatter mode.

In addition to recovering a clock, the clock recovery and data recoverycircuit 38 also performs data recovery on valid incoming signals. Thevalid spread spectrum incoming signal is passed through the spreadspectrum processing circuit 40 which extracts the actual ones and zerosof data from the incoming signal. More particularly, the spread spectrumprocessing circuit 40 takes chips from the spread spectrum signal andreduces individual thirty-one chip sections down to a bit of one orzero, which is passed to microcontroller 34.

Microcontroller 34 includes a serial processor, or I/O, facility thatreceives the bits from spread spectrum processing circuit 40. Themicrocontroller 34 performs further error correction. More particularly,a modified hamming code is employed, wherein each eight bits of data isaccompanied by five check bits used by the microcontroller 34 for errorcorrection. Microcontroller 34 further includes a memory, and afterperforming the data correction, microcontroller 34 stores bytes of thedata bits in memory. These bytes contain a command sent by theinterrogator 26. Microcontroller 34 is configured to respond to thecommand.

For example, interrogator 26 may send a command requesting that anycommunication device 12 in the field respond with the device'sidentification number. Status information can also be returned tointerrogator 26 from remote communication devices 12. Additionally,remote communication devices 12 may be individually coupled with aperipheral device and information regarding the peripheral device mayalso be communicated.

Communications from interrogator 26 (i.e., forward link communications)and devices 12 (i.e., return link communications) have a similar format.More particularly, the forward and return communications individuallyinclude a calibration period, preamble and Barker or start code whichare followed by actual data in the described embodiment. The incomingforward link message and outgoing return preferably also include a checksum or redundancy code so that transponder 16 or interrogator 26 canconfirm receipt of the entire forward message or return message.

Communication devices 12 typically include an identification sequenceidentifying the particular tag or device 12 sending the return linksignal. Such implements the identification operations of communicationsystem 10.

After sending a command, interrogator 26 sends the unmodulatedcontinuous wave signal. Return link data can be Differential Phase ShiftKey (DPSK) modulated onto the continuous wave signal using a square wavesubcarrier with a frequency of approximately 600 kHz (e.g., 596.1 kHz inone embodiment). A data 0 corresponds to one phase and data 1corresponds to another, shifted 180 degrees from the first phase.

The subcarrier or modulation signal is used to modulate antennaimpedance of transponder 16 and generate the modulated continuous wavesignal. For a simple dipole, a switch between the two halves of thedipole antenna is opened and closed. When the switch is closed, theantenna becomes the electrical equivalent of a single half-wavelengthantenna that reflects a portion of the power being transmitted by theinterrogator. When the switch is open, the antenna becomes theelectrical equivalent of two quarter-wavelength antennas that reflectvery little of the power transmitted by the interrogator. In oneembodiment, the dipole antenna is a printed microstrip half-wavelengthdipole antenna.

Referring to FIG. 5, one embodiment of interrogator housing 14 and theinternal circuitry therein is illustrated. The depicted interrogatorhousing 14 generally includes a microcontroller 70, a field programmablegate array (FPGA) 72 and RF section 74. In the depicted embodiment,microcontroller 70 comprises a MC68340 microcontroller available fromMotorola, Inc. FPGA 72 comprises an XC4028 device available from Xilinx,Inc. Further details of components 70, 72 and 74 are described below.

Interrogator housing 14 also includes RAM 76, EPROM 78 and flash memory80 coupled with microcontroller 70 in the depicted embodiment.Microcontroller 70 is configured to access an applications program fromEPROM 78 for controlling the interrogator 26 and interpreting responsesfrom remote communication devices 12.

The processor of microcontroller 70 is configured to controlcommunication operations with remote communication devices 12 duringnormal modes of operation. The applications program can also include alibrary of radio frequency identification device applications orfunctions. These functions effect radio frequency communications betweeninterrogator 26 and associated remote communication devices 12.

Microcontroller 70 includes circuitry configured to generate forwardlink communication signals to be communicated to remote communicationdevices 12. Further, microcontroller 70 is also configured to processreturn link communication signals received from remote communicationdevices 12. Alternatively, an external processor or computer (not showncan be coupled with interrogator 26 to process the return linkcommunication signals.

RF section 74 is configured to implement wireless (e.g., radiofrequency) communications with remote communication devices 12. DPSKmodulation techniques can be utilized for communications intermediatedevices 12 and interrogator 26. RF section 74 can include downconversioncircuitry for generating in-phase (I) and quadrature (Q) signals whichcontain the DPSK modulated subcarrier for application to FPGA 72 duringreturn link communications.

Analog to digital (A/D) converters 82, 84 provide received analog RFsignals into a digital format for application to FPGA 72. In particular,analog to digital converters 82, 84 are implemented intermediate FPGA 72and RF section 74 for both in-phase (I) and quadrature (Q) communicationlines.

An additional connection 85 is provided intermediate FPGA 72 and RFsection 74 for forward link communication signals. Digital signals to becommunicated from interrogator 26 are outputted from FPGA 72 viaconnection 85 and converted to RF forward link communication signals byRF section 74. Connection 85 can additionally be utilized to transmitphase lock loop (PLL) information and other necessary communicationinformation. During forward link communications, FPGA 72 is configuredto provide communication packets received from microcontroller 70 into aproper format for application to RF section 74 for communication.

FPGA 72 is configured to demodulate return link communications receivedfrom remote communication devices 12 via RF section 74. FPGA 72 isconfigured in the described embodiment to perform I and Q combinationoperations during receive operations. The described FPGA 74 furtherincludes delay and multiplication circuitry to remove the subcarrier.FPGA 74 can also include bit synchronization circuitry and lockdetection circuitry. Data, clock and lock detection signals generatedwithin FPGA 74 are applied to microcontroller 70 for processing in thedescribed embodiment.

Microcontroller 70 is configured to control operations of interrogator26 including outputting of forward link communications and receivingreturn link communications. EPROM 78 is configured to store originalapplications program codes and settings selected for the particularapplication of communication system 10. Flash memory 80 is configured toreceive software code updates which may be forwarded to interrogator 26.

RAM device 76 is configured to store data during operations ofcommunication system 10. Such data can include information regardingcommunications with associated remote communication devices 12 andstatus information of interrogator 26 during normal modes of operation.

In accordance with the described embodiment, RF section 74 ofinterrogator housing 14 is coupled with plural communication circuits106 as shown in FIG. 1. Microcontroller 70 is configured to select anappropriate communication circuit 106 to implement forward link andreturn link communications with desired remote communication devices 12within respective communication ranges 15. RF section 74 includesswitching circuitry configured to selectively couple one ofcommunication circuits 106 with RF circuitry within RF section 74 aswell as connection 85 and analog to digital converters 82, 84. Suchswitching is controlled by microcontroller 70 depending upon theindividual communication range 15 presently communicating withinterrogator 26.

For example, microcontroller 70 can initially select one ofcommunication paths 17 to provide communications of interrogator 26 withremote communication devices 12 within the communication range 15 whichcorresponds to the originally selected path 17. Thereafter,microcontroller 70 can select another one of communication paths 17using switching circuitry of RF section 74 to provide communications ofinterrogator 26 with remote communication devices 12 within thecommunication range 15 which corresponds to the newly selected path 17.

Exemplary switching operations of the communication paths 17 can beperformed under control of microcontroller 70 after individual forwardlink communications to respective communication paths 17 andcorresponding communication ranges 15 occur in one operational mode.Alternatively, microcontroller 70 can switch communication paths 17after forward link communications and return link communications occurwith a desired communication range 15. Other communication switchingprotocols can be utilized in other configurations.

Referring to FIG. 6, an exemplary configuration of RF circuitry 74 isillustrated. The depicted RF circuitry 74 includes a transmit path 86and a receive path 87. Communication paths 86, 87 are coupled with RFcontrol circuitry 97. Transmit path 86 is additionally coupled with FPGA72 shown in FIG. 5 via connection 85. Receive path 87 is coupled withanalog to digital converters 82, 84 shown in FIG. 5 via the I and Qconnection lines.

Forward link communication signals are communicated via path 86 whilereturn link communication signals are communicated via path 87. In thedepicted embodiment, RF section 74 additionally includes a transmitter90 and driver amplifier 92 within transmit data path 86. Receive path 87includes a receiver 95 and adjustment circuitry 96 in the describedembodiment.

Transmitter 90 is configured to implement radio frequency modulationoperations in the described embodiment using the forward linkcommunication signal previously generated. The modulated forward linkcommunication signal outputted from transmitter 90 is applied to driveramplifier 92. Driver amplifier 92 is configured to increase the powerlevel of the forward link communication signal. In typicalimplementations, driver amplifier 92 is configured to provide a gain ofapproximately 10-15 dB. Amplifiers providing more or less gain may beutilized depending upon the specific application and expected losswithin communication circuitry 106.

Thereafter, driver amplifier 92 applies the amplified forward linkcommunication signal to an input of a selected communication circuit 106responsive to control from microcontroller 70 and using RF control 97.In the described configuration, RF control 97 comprises switchingcircuitry configured to selectively couple transmit path 86 and receivepath 87 with a selected one (or ones) of communication circuitry 106. RFcontrol 97 implements the switching operations to selectively couplecommunication circuits 106 with transmit path 86 and receive path 87responsive to control from microcontroller 70.

Depending upon the particular application for use of communicationsystem 10 or location of associated communication stations 120,communication circuits 106 can be individually implemented in one of avariety of configurations. Communication circuits 106 are locatedoutside of interrogator housing 14 and are coupled with driver amplifier92 and adjustment circuitry 96 via RF control 97. Communication circuits106 are individually configured to communicate the forward linkcommunication signals and return link communication signals within thecorresponding communication path 17 intermediate housing 14 and thecorresponding communication station 120.

In some embodiments, communication circuits 106 individually comprisecoaxial RF cable. Depending upon the distance intermediate housing 14and the corresponding communication station 120, low-loss coaxial RFcable may be utilized. Further, amplifiers having increased gain may beutilized in addition to the described amplifiers to increase the powerlevel of the forward link communication signals and return linkcommunication signals being communicated within communication circuitry106. Various combinations of components can be utilized depending uponthe particular application and associated loss to ensure that theforward link communication signals and return link communication signalsoutputted from communication circuitry 106 are at a power levelsufficiently above the thermal noise.

Referring to FIG. 7, an alternative configuration of communicationcircuitry 106 which may be utilized within individual communicationpaths 17 is illustrated. The depicted communication circuitry 106includes a plurality of transceivers 108, 109 individually coupled withone of interrogator housing 14 and one of communication stations 120.Transceivers 108, 109 operate to communicate forward link communicationsignals and return link communication signals intermediate interrogatorhousing 14 and the corresponding communication station 120. In anexemplary configuration, transceivers 108, 109 are configured tocommunicate utilizing electromagnetic signals, such as radio frequencysignals. Such signals are preferably communicated outside of thefrequency band of forward link wireless signals 27 and return linkwireless signals 29.

Referring to FIG. 8, an exemplary embodiment of one of communicationstations 120 is illustrated. The depicted communication station 120 iscoupled with communication circuitry 106. The depicted communicationstation 120 includes transmit circuitry 121 and receive circuitry 123.Transmit circuitry 121 is coupled with the X1 antenna 126 and receivecircuity 123 is coupled with the R1 antenna 128. One configuration oftransmit circuitry 121 is described with reference to FIG. 8, and oneconfiguration of receive circuitry 123 is described with reference toFIG. 9.

The depicted transmit circuitry 121 shown in FIG. 8 includes adjustmentcircuitry 122, a power amplifier 124 and a potentiometer 137. Forwardlink communication signals received from communication circuitry 106 areapplied to transmit circuitry 121. Forward link wireless signals 27corresponding to the forward link communication signals are radiatedusing antenna 126. Return link wireless signals 29 are received by R1antenna 128 and applied to receive circuitry 123. Receive circuitry 123outputs return link communication signals corresponding to the returnlink wireless signals to communication circuitry 106.

Referring to transmit operations, forward link communication signalsfrom communication circuitry 106 are initially applied to adjustmentcircuitry 122 within transmit circuitry 121. Adjustment circuitry 122 isconfigured to receive the forward link communication signals fromcommunication circuitry 106 and to adjust at least one electricalcharacteristic of the forward link communication signals. In anexemplary configuration, adjustment circuitry 120 is configured toadjust the power level of the forward link communication signal.

More specifically, the depicted adjustment circuitry 122 comprisesautomatic gain control (AGC) circuitry. In particular, the automaticgain control circuitry is configured to monitor the power of the forwardlink communication signals, compare the power with a predeterminedthreshold value and adjust the power of the forward link communicationsignals responsive to the comparison.

Adjustment circuitry 122 comprising automatic gain control circuitryincludes a variable gain amplifier 130, a coupler 132, a detector 134and a loop filter 136 in an exemplary configuration. Forward linkcommunication signals received from communication circuitry 106 areapplied to coupler 132. Coupler 132 directs a portion of the power ofthe forward link communication signals to detector 134 which convertsthe received power into a voltage.

The converted voltage is directed to loop filter 136. Loop filter 136 isadditionally coupled with a potentiometer 137 in the describedconfiguration. Potentiometer 137 can be utilized to provide anadjustable threshold reference voltage. Potentiometer 137T may be variedto fine tune individual communication stations 120 depending upon thedistance intermediate the communication station 120 and interrogatorhousing 14 (e.g., the threshold reference voltage can be varied toaccommodate varying amounts of loss intermediate individualcommunication stations 120 and the corresponding interrogator housing14).

A Loop filter 136 compares the received voltage from detector 134representing the power level of the received forward link communicationsignals with the adjustable reference voltage determined bypotentiometer 137. Thereafter, loop filter 136 outputs a control signalto variable gain amplifier 130 to adjust the power of the forward linkcommunication signals applied to power amplifier 124 responsive to thecomparison.

Preferably, variable gain amplifier 130 provides forward linkcommunication signals to power amplifier 124 which have a substantiallyconstant input power level as determined by potentiometer 137. Such ispreferred to provide linear operation of power amplifier 124. Poweramplifier 124 amplifies the forward link communication signals. It ispreferred to provide forward link communication signals of approximately1 mW to power amplifier 124 which comprises a 1 watt amplifier in oneembodiment operable to provide approximately 30 dB of gain.

The output of power amplifier 124 is applied to the X1 antenna 126.Preferably, the distance intermediate power amplifier 124 and the X1antenna 126 is minimized. X1 antenna 126 is operable to receive theamplified forward link communication signals 27 from power amplifier 124and to radiate forward link wireless signals 27 corresponding to theforward link communication signals. X1 antenna 126 of the correspondingcommunication station 120 is preferably positioned to radiate theforward link wireless signals 27 within at least one of the plurality ofcommunication ranges 15.

Referring to FIG. 9, details of receive circuitry 123 are illustrated.Receive circuitry 123 is coupled with communication circuitry 106 and R1antenna 128. The illustrated receive circuitry 123 includes a low noiseamplifier (LNA) 140 coupled with an amplifier 142. The R1 antenna 128 iscoupled with low noise amplifier 140. R1 antenna 128 receives returnlink wireless signals 29 from remote communication devices 12 locatedwithin one or more of communication ranges 15. Antenna 128 outputsreturn link communication signals corresponding to the return linkwireless signals 29 to low noise amplifier 140.

Preferably, the distance intermediate the R1 antenna 128 and the lownoise amplifier 140 is minimized. The low noise amplifier 140 isconfigured to receive the return link communication signals and increasethe power of the return link communication signals. Such amplificationpreferably increases the level of the return link communication signalsto a sufficient degree above the thermal noise.

The return link communication signals are thereafter applied to 41amplifier 142 which has a gain to further increase the power level ofthe return link communication signals. In an exemplary configuration,amplifiers 140, 142 individually have a gain of approximately 15 dB.Receive circuitry 123 is merely exemplary and can be configured toprovide more or less gain depending upon the expected loss withincommunication circuitry 106. In one configuration, amplifier 142 alsocomprises a low noise amplifier.

Preferably, receive circuitry 123 and communication circuitry 106 areconfigured to provide return link communication signals to theinterrogator housing 14 having a sufficient signal-to-noise ratio. Aspreviously described, communication circuitry 106 comprising coaxial RFcable, transceivers or other configurations communicates the return linkcommunication signals to interrogator housing 14.

Referring to FIG. 10, return link communication signals received withincommunication station 120 and communicated using communication circuitry106 are applied to RF control 97 within interrogator housing 14. RFcontrol 97 operates to selectively couple one of communication circuits106 with receive path 87 responsive to control from microcontroller 70as described above.

Return link communication signals from RF control 97 are applied toadjustment circuitry 96 within housing 14. Adjustment circuitry 96 isconfigured to receive the return link communication signals from RFcontrol 97 and to adjust at least one electrical characteristic of thereturn link communication signals. In an exemplary configuration,adjustment circuitry 96 is configured to adjust the power level of thereturn link communication signals.

More specifically, the depicted adjustment circuitry 96 comprisesautomatic gain control (AGC) circuitry. The automatic gain controlcircuitry is configured to monitor the power of the return linkcommunication signals, compare the power with a threshold value andadjust the power of the return link communication signals responsive tothe comparison.

Adjustment circuitry 96 comprising automatic gain control circuitryincludes a variable gain amplifier 150, a coupler 152, a detector 154and a loop filter 156. Return link communication signals received fromRF control 97 are applied to variable gain amplifier 150 which adjuststhe power level of the return link communication signals responsive tocontrol from loop filter 156. Coupler 152 directs a portion of the powerof the return link communication signals to detector 154 which convertsthe received power into a voltage. The converted voltage is directed toloop filter 156.

Loop filter 156 compares the received voltage from detector 154representing the power level of the return link communication signalswith a reference voltage. Thereafter, loop filter 156 outputs a controlsignal to variable gain amplifier 150 which adjusts the power of thereturn link communication signals applied to receiver 95 responsive tothe comparison. Although not shown, circuitry may be provided to permitadjustment of the reference voltage of loop filter 156 similar to thatof potentiometer 137 of communication station 120.

Preferably, variable gain amplifier 150 provides return linkcommunication signals to receiver 95 which have a substantially constantor fixed input level. In one embodiment, adjustment circuitry 96 isconfigured to output rerun link communication signals having a powerlevel of approximately 3 dBm. Such is preferred to avoid saturation ofcomponents (e.g., downconversion circuitry) within receiver 95. Thereturn link communication signals may be processed by microcontroller 70or other circuitry following demodulation of the return linkcommunication signals.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. An interrogator of a radio frequencyidentification system comprising: a plurality of communication stationsindividually including: a first antenna configured to output a forwardlink wireless signal; a second antenna configured to receive a returnlink wireless signal responsive to the outputting of the forward linkwireless signal and to output a return link communication signalcorresponding to the return link wireless signal; and a low noiseamplifier coupled with the antenna and configured to increase the powerof the return link communication signal; a plurality of coaxial RFcables coupled with the low noise amplifiers of the respectivecommunication stations and individually configured to communicate thereturn link communication signal of the respective communicationstation; and a housing remotely located with respect to thecommunication stations and including: a plurality of automatic gaincontrol circuits coupled with respective ones of the coaxial RF cablesand configured to adjust at least one electrical characteristic of therespective return link communication signals to output the return linkcommunication signals at a substantially constant level; and processingcircuitry configured to receive the return link communication signalsfrom the automatic gain control circuits and to process the return linkcommunication signals.